ImageData

ImageData is a data structure used to store raw pixel information for a rectangular region of an image or drawing surface. In many programming environments, it represents pixels as a flat, one‑dimensional array of color components in RGBA order, with one byte per channel. ImageData does not encode image file metadata or compression; it is the in-memory depiction of pixel colors.

The ImageData object exposes three main properties: data, width, and height. The data property is a Uint8ClampedArray whose length equals width × height × 4. For each pixel, four consecutive values represent red, green, blue, and alpha. The alpha channel defines opacity, ranging from 0 (fully transparent) to 255 (fully opaque). Values are clamped to the 0–255 range.

Creation and access typically occur in canvas-based web APIs. ImageData can be created directly with new ImageData(width, height) for a blank image, or obtained from a drawing surface via context.getImageData(x, y, w, h). Modified pixel values in the data array are reflected when the image data is drawn back to a canvas with putImageData. A common indexing pattern to access a pixel at coordinates (x, y) is i = (y × width + x) × 4, then red at data[i], green at data[i+1], blue at data[i+2], and alpha at data[i+3].

ImageData is widely used for pixel-level image processing, such as applying filters, adjusting brightness, or performing compositing. While the web standard often centers on RGBA 8‑bit per channel data, other environments may store pixel data in different orders or precisions. Regardless, ImageData serves as the raw pixel buffer behind rendered images.